The handling of radioactive plutonium oxide, and its safe long-term storage and subsequent reprocessing or disposal pose significant challenges to the nuclear industry. There is evidence of gas build-up in storage containers, which may be due to small residual molecules, including water, hydrogen and products of radiolysis. Knowledge on the interaction of such species with the surface of the oxide will aid handling of the long-term storage of PuO2. In our study, we used Density Functional Theory calculations (PBEsol + U) including the effect of spin-orbit interactions coupled with the complex 3k antiferromagnetic longitudinal ordering to understand the surface composition and energetics of PuO2 surfaces when water, carbon dioxide and hydrogen peroxide are adsorbed. We found that strong chemical adsorption is favoured. Water and hydrogen peroxide dissociate while carbon dioxide forms surface carbonate groups on all the most relevant PuO2 surfaces including the {111}, {110} and {100} surfaces. Finally, we used a thermodynamic strategy to evaluate the surface free energy of adsorbed surfaces, from which we mapped the PuO2 surface phase diagrams as a function temperature, water and oxygen partial pressure. These free energies have also been used to predict equilibrium nanoparticle morphologies and infer how external conditions may drive particle morphology evolution between the polyhedral shaped nanocubes, truncated octahedra and octahedra.

Adsorption of water, carbon dioxide and hydrogen peroxide on PuO2 surfaces: A density functional theory study

ACS Spring Meeting 2021

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